Referential alarm calls occur across taxa to warn of specific predator types. However, referential calls may also denote other types of dangers. Yellow warblers (Setophaga petechia) produce “seet” calls specifically to warn conspecifics of obligate brood parasitic brown-headed cowbirds (Molothrus ater), which lay their eggs in the warblers’ and other species’ nests. Sympatric hosts of cowbirds that do not have referential alarm calls may eavesdrop on the yellow warbler’s seet call as a warning system for brood parasites. Using playback presentations, we found that red-winged blackbirds (Agelaius phoeniceus) eavesdrop on seet calls of yellow warblers, and respond as much to seet calls as to cowbird chatters and predator calls. Red-winged blackbirds appear to eavesdrop on seets as warning system to boost frontline defenses on their territories, although they do not seem to perceive the warblers’ seets as a cue for parasitism per se, but rather for general danger to the nest.

在整个分类单元中发生参考警报呼叫，以警告特定的捕食者类型。但是，引用呼叫也可能表示其他类型的危险。黄莺（Setophaga petechia）发出“ seet”号，特别是警告那些专性亲虫寄生的棕头牛鸟（Molothrus ater），它们将卵产在莺和其他物种的巢中。没有参考警报电话的牛patri同胞寄主可能会偷听黄色鸣鸟的蜂鸣电话，作为对巢内寄生虫的预警系统。通过回放演示，我们发现了红翅黑鸟（Agelaius phoeniceus）窃听黄莺鸣叫的声音，并且对鸣叫做出的响应与对牛bird的and叫和掠食者的鸣叫一样多。红翅黑鸟似乎偷听了种子，以此作为加强其领土前线防御的预警系统，尽管它们似乎并不认为鸣鸟的种子本身是寄生虫的线索，而是对巢穴的一般危险。